The application of labels to articles and products has been and continues to be an important step in providing product identification, specific product information and marketing advantages. Manufacturers of various products are continually seeking a more efficient and effective manner in which to apply labels to articles or items, such as cartons, containers or any other packages or products Laving a surface capable of securely receiving an adhesive label.
Numerous methods have been employed in the past to mark articles, such as color-coded ink sprays and manually applied stickers. The introduction of adhesive-backed pressure sensitive labels and hand-held, manually operated applicators has greatly facilitated the marking of articles in that the applicators provide a simple means for applying an adhesive-backed label to an article. Such hand-held label applicators are well known and used extensively in various industries, for example, for marking the price of articles to be sold. Their use, however, in manufacturing, assembling and distributing applications is limited because of the necessity for marking many items at a high rate of speed. In these applications, the articles to be labeled are transported along a conveyor past a number of stations, one of which often entails the application of a label to each article as it passes by or while the conveyor is stopped. Use of a hand-held label applicator in this type of high speed operation would be unacceptably slow, inefficient, labor intensive and therefore, inipractical due to the time constraints associated with high volume production.
As a result, relatively high speed labeling machines have been developed to apply labels to articles advancing by a labeling station on, for example, a conveyor belt. The pressure-sensitive labels are commonly precut and carried on a continuous web of material often called backing material which is rolled into a roll for mounting on the labeling machine. The backing material is somewhat more flexible than the label itself. This allows the label to be separated from the backing material, or dispensed, simply by bending the backing material sharply away from the label, which is usually done by drawing the backing over a fairly sharp stripping or peeling edge of a peeling bar or plate. The less flexible label then separates from the backing material and remains relatively straight for application to the article by some type of applicator. For example, U.S. Pat. Nos. 3,321,105 to Marano and 5,022,954 to Plaessmann disclose automated labeling machines which operate at relatively high speed when compared to manual application.
Although some present labeling machines function adequately at certain high speeds, there is an ongoing need for labeling machines capable of labeling at extremely high speeds so as to increase the number of labels applied per unit time, thereby increasing the efficiency of the manufacturing process. One method of increasing the labeling capacity of a machine is to increase the speed at which the web moves through the machine. The higher the moving or feed speed of the web through the machine, the greater the number of labels dispensed per unit time. A common form of driving means for pulling the web through the labeling machine is a nip roller assembly driven by, for example, a stepper motor such as disclosed in both Marano '105 and Plaessmann '954. The web passes through a nip formed between a driver roller, powered by the stepper motor, and a driven or nip roller biased against the driver roller. In this manner, the rollers engage the web so that intermittent operation of the stepper motor causes intermittent movement of the web through the labeling machine. Increasing the speed of the stepper motor will, therefore, increase the speed of the web through the dispenser, i.e., over the peeler bar. However, the web feed speed will certainly be limited by the maximum operational speed and capacity of the driver of the nip roller assembly. Although a single driving device, such as a stepper motor, capable of achieving higher speeds and torque capacities, may be available, these drivers are often too large and too expensive. Therefore, it has been found that many labeling machines are incapable of achieving extremely high labeling speeds while minimizing costs. Moreover, as with the labelers disclosed in Marano '105 and Plaessmann '954, the nip roll assembly is often used as both a driving means and a metering means. In this instance, the driver roller must function to both pull the web through the machine while also stopping and starting the movement of the web so as to properly meter the correct length of web over the peeler bar as required to dispense the next label(s). However, the ability of the nip roll assembly to accurately and effectively meter the proper length of web is impaired, especially at high speeds, by the requirement of the assembly to also provide the pulling force necessary to pull the web through the machine. As a result, at very high speeds, these driving and metering nip roll assemblies often fail to provide accurate and effective metering of the web.
The labeling machines disclosed in Marano '105 and Plaessmann '954 include a tensioning device downstream of the metering roll for maintaining a continuous tension in the web between the metering roll and a take-up drum. Specifically, the Marano tensioning device is a slipping belt/pulley arrangement attached to a take-up drum for continually rotating the take-up drum with a light rotational load. The Plaessmann reference discloses an idler arm-type assembly positioned between the metering roll and take-up drum for applying a light tensioning load to the web. In both embodiments, the tensioning device functions as a speed compensator between the take-up drum and the metering roll which do not move in complete synchronization. In this manner, the slip belt/pulley device and the idler arm device both insure that there are no loops or kinks in the web before it goes to the take-up drum by maintaining a continuous tension in the web. However, the continuous tension in the web caused by these tensioning devices varies throughout the operation of the labeling machine. As the web material accumulates on the take-up drum, the diameter of the take-up roll of material gradually increases, thereby continually increasing the moment arm through which the accumulating force of the take-up drum acts on the web. As a result, the force applied on the web by the take-up drum gradually decreases as the diameter of the roll increases, thus gradually decreasing the tension in the web. Also, the spring force biasing the idler arm of the Plaessmann '954 device varies throughout movement of the arm thus varying the tension in the web. Moreover, the continuous stopping and starting of the metering roll causes variations in the web tension downstream of the metering roll. These variations in web tension downstream of the driving and metering roll cause undesirable variations in web tension through the labeling machine. These tension variations adversely affect the ability of the metering roll to accurately and effectively meter the web thereby also adversely affecting ihe dispensing of labels by, for example, failing to pull the proper length of web across the peeler bar. Moreover, the web tension variations felt upstream at the peeler bar disadvantageously affect the dispensing of labels by making it more difficult for the metering means to accurately and repeatedly pull the web over the peeler bar with the optimum amount of constant web tension necessary for effective dispensing of labels at a given web speed. In addition, the above-noted adverse affects of web tension variations are exacerbated at higher web speeds at which substantially constant web tension becomes critical to achieving accurate metering and dispensing of labels.
Many labeling machines also include a printing device upstream of the dispenser for printing indicia on the labels as the web passes through the printer. The printing devices used are often "off-the-shelf" items having a metering/driving roll incorporated therein. As a result, it is often more cost effective and easier to use this existing metering/driving roll as the primary metering/driving roll for the labeling machine. However, the driver for the driving/metering roll found in many printers often lacks the power/torque capable of: 1) accurately metering the web at higher web speeds while maintaining high printing quality; and/or 2) creating a pulling force sufficient to overcome the inertia of a large supply roll of continuous web, as used in large capacity labeling, so as to effectively pull the web from the supply roll while accurately metering the web.